Heat pipe

ABSTRACT

A heat pipe in which a vapor duct is mounted in the heat output zone to separate the vaporized working medium from the capillary walls of the heat output zone while the vapor is moving in a direction opposite to fluid capillary motion in the walls.

tput zone while the posite to fluid capillary mo l/1966Grover.........................

FOREIGN PATENTS 8/1942 Germany...................... 8/1948 GreatBritain..... 5/1958 OTHER REFERENCES Sandia Laboratories Heat PipeConference, Vol. 10/1966, Sandia Corp., Albuquerque, NM. pp. 12 and 24SC- M-66-623 (91 pages) pe in which a vapor duct is mounted in toseparate the vaporized working medi- Glenn H. Bruestle Willis E.Harbaugh Leola,Pa. [21] AppLNo. 640,693 [22] Filed References CitedUNITED STATES PATENTS 308,197 11/1884 Rober.........,.................3,217,791 11/1965 May 23, 1967 RCA Corporation 8 Claims, 1 Drawing Fig.

United States Patent [72] Inventor [45] Patented Mar, 9, 1971 [73]Assignee [54] HEAT PIPE [51] Int. [50] Field /7/////////J7////////////VA HEAT PIPE BACKGROUND OF THE INVENTION 1. Field of the Invention Theinvention relates in general to an improved heat transfer apparatus andparticularly to improved heat pipe apparatus which provides improvedheat transfer efficiency.

2. Description of the Prior Art I A heat pipe is a vapor device which isused to convey heat from a heat source to a heat output or dissipationzone. Such a device is described in general terms in an article entitledStructures of Very High Thermal Conductance by G/M. Grover in Volume 35of the Journal of Applied Physics, pages 1990 and 1991. The heat pipeusually comprises a closed tubular structure having a lining ofcapillary material and a vaporizable heat transfer or working mediumtherein. The capillary lining can consist of wire cloth, porous matrixmaterials or channeling in the walls of the heat pipe itself. Theworking medium is selected to have a vaporization temperature equal tothe desired operating temperature of the heat pipe. For example, lithiummay be used as a working medium for high temperature applications andwater can be used for lower operating temperatures. For most efficientoperation all undesirable foreign-gases are removed from the heat pipeenvelope and the working medium.

Before heat is applied, preferably substantially all of the workingmedium is present in liquid form in the capillary walls of the heatpipe. Heat is applied from a heat source to the heat input zone of theheat pipe causing the liquid working medium in the capillary walls ofthis zone to vaporize and fill the interior of the heat pipe. Thevaporized medium expands and then condenses on the inner walls of theheat output or heat dissipation zone of the heat pipe, giving up itslatent heat of vaporization. The condensed liquid working medium is thentransported by capillary action along the heat pipe wall from the heatoutput zone to the heat input zone to fill the area vacated by thevaporized working medium. In this way heat is transferred from a heatsource to a heat output zone while the working medium is circulatedthrough the heat pipe. Since the heat pipe is a closed system and has nomoving parts to wear out, it is useful for applications such as spacewhere maintenance is difficult. Heat pipes are also useful in enclosedspaces and in airless environments where other cooling techniques aredifficult to use.

In priorart heat pipes, some loss in heat pipe efficiency resulted fromthe friction occurring between the vaporized working medium which movesfrom the heat input zone to the heat output zone of the heat pipe andthe fluid working medium which moves along the walls of the heat pipefrom the heat output zone to the heat input zone. These opposing flowstend to retard each other along the capillary walls of the heat outputzone.

SUMMARY OF THE INVENTION The foregoing problems of oppositely flowinggaseous and liquid media are overcome by an improved heat pipe whichincludes a vapor duct mounted to'extend into the heat output zone of theheat pipe and arranged so that substantially all the vaporized workingmedium must pass through it to reach the remote end of the heat outputzone of the heat pipe. The vapor is thus separated from the capillaryinner walls of the heat output zone while it is moving in a directionopposed to the liquid flow in these walls. The vapor duct is open atboth ends allowing the vapor to leave the duct at the remote end of theheat output zone. The end of the heat pipe in the heat output zone has areentrant arch of rotation configuration which smoothly reverses thevapor flow and directs the vapor close to the capillary walls of theheat output zone where it condenses. In this way vapor flow is insubstantially the same direction as liquid flow when the vaporizedworking medium reaches the capillary walls of the heat'output zone.

Heat pipes incorporating the invention can be used to convey heat from aheat source to an area where the heat is utilized or dissipated. If heatdissipation is desired, fins or other radiating means can be attached tothe exterior of the heat output zone of the heat pipe. For example, heatpipes can be used to cool an electron tube and other heat sources or totransfer heat to components in the cold environments of space or to athermoelectric generator from a radioactive source or other heat source.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectionalview of a preferred embodiment of the improved heat pipe;

FIG. 2 is a sectional view taken along the line 1-1 of FIG. 1; and vFIG. 3 is a longitudinal sectional view of a second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The outer envelope 10 of theheat pipe preferably is a tubular structure closed at both ends. It canbe constructed of any suitable good heat conducting material. Molybdenumis often used for high temperature heat pipes and copper for those whichoperate at lower temperatures. A lining 12 of capillary material coversthe entire inside surface of the heat pipe. This lining can be wire meshscreening, a porous matrix material, or even can be channeling in thewalls of the heat pipe. The heat pipe is divided into two zones, a heatinput zone 14 and a heat output or dissipation zone 16.

A funnel-shaped vapor duct 18 is mounted to extend into the heat outputzone 16 of the heat pipe. It is preferably fabricated of the same metalas the outer envelope 10. The duct 18 consists of a pipelike structureof a uniform diameter over most of its length which diameter issubstantially less than the inner diameter of the capillary lining 12.The end 20 of the duct 18 adjacent to the heat input zone 14 is flaredoutwardly so that its outer edge is in contact with the capillary lining12 along a line 22 at the approximate dividing line between the heatinput zone 14 and the heat output zone 16; The relatively narrower end21 of the vapor duct 18 is located adjacent to the remote end 24 of theheat output zone of the heat pipe. This narrow end 21 of the vapor duct18 has a rim 25 which extends outwardly and curves downwardly to inhibitthe vaporized working medium from flowing down the sides of the vaporduct 18 and to direct it relatively close to the capillary walls 12. Theremote end of the heat pipe 24 in the heat output zone is formed by areentrant arch of rotation about a point 26 located adjacent to andcoaxially with the center of the narrow end 21 ofthe vapor duct 18.

To retain the vapor duct 18 at a proper position in the heat pipe, theouter edge of its flared end 20 is attached to the capillary lining 12of the heat pipe along a line 22 by welding or other appropriate means.Further mechanical stability is provided, if desired, by the addition ofthree rigid metal radial braces 27 extending from the capillary lining12 to the vapor duct 18 at points 28 adjacent to the narrow end 21 ofthe duct as shown in FIG. 2. These braces 27 are usually fabricated ofthe same material as the body of the vapor duct 18 and may be made anintegral part of the duct 18. The outer ends of the radial braces 27 arein contact with or may be fastened to the capillary lining 12 of theheat pipe walls by welding or other suitable means.

The second embodiment of the invention shown in FIG. 3 has an adiabaticzone 34 between the heat input zone 14 and the heat output zone 16. Thetemperature remains substantially constant in the adiabatic zone, andthe capillary lining 12 is in this zone need not be free to releasevapor or absorb condensing liquid. In this embodiment. the vapor duct 18terminates in a sleeving 38 at its flared end 20. This sleeving 38constitutes a part of the vapor duct 18 and has a diameter large enoughto fit tightly against the capillary lining 12 in the adiabatic zone 34.The sleeving 38 is attached to the capillary walls 12 of the heat pipeby welding or other suitable means. This will provide adequatemechanical support for the vapor duct 18 without further bracing. Otherfeatures of this embodiment are identical to those described for thefirst preferred embodiment.

In either embodiment heat is applied to the heat input zone 14 causingthe working medium contained in the capillary walls 12 to vaporize andexpand throughout the heat pipe. The vaporized working medium 40 isforced to move through the vapor duct 19 since the flared end 20 of thevapor duct 18 completely blocks off other portions of the interior ofthe heat pipe. The vapor 40 moves through duct 18 and passes out of theduct at the narrow end 21. The curved rim 25 around the narrow end 21 ofthe vapor duct 13 and the reentrant arch of rotation configuration ofthe end 24 of the heat pipe smoothly reverses the flow of the vaporizedworking medium 40 so that most of the vapor flows close to the capillarywalls 12 of the heat output zone 16 where it condenses on the capillarywalls 12. Both the vaporized working medium and the liquid in thecapillary walls flow in substantially the same direction in the heatoutput zone 16. Liquid working medium then moves through the capillarywalls from the heat output zone 16 to the heat input zone 14 to fillareas vacated by the heated vaporized working medium 40.

The vapor duct 18 provides more efficient circulation of the workingmedium because the vaporized working medium 40 moving toward the heatoutput zone 16 is separated from the capillary walls 12 of the heatoutput zone 16 in which liquid working medium is moving in the oppositedirection. Without the vapor duct 18 these opposing flows would tend toretard each other decreasing the heat transfer capability of the heatpipe.

Little of the efficiency of the capillary walls 12 is lost by attachingthe vapor duct 18 to them. Liquid working medium moves past line 22where the vapor duct is attached to the capillary walls through theinterior portions of the capillary lining to react the heat input zone14 of the heat pipe.

I claim:

1. A heat pipe comprising:

a. a hollow envelope having a sealed wall structure, said wall structureincluding a heat input zone and a heat output zone;

b. capillary means contiguously disposed on at least a portion of theinner surface of said wall structure, said portion including said heatinput zone and said heat output zone;

c. a working medium within said envelope vaporizable below the operatingtemperature of said heat pipe; and

d. a vapor duct mounted within said envelope, said vapor duct having alarger end adjacent to the boundary between said heat input and saidoutput zones and contiguous with said capillary means, and a narrowerend located adjacent to the enclosed end of said heat pipe in said heatoutput zone.

2. A heat pipe as described in claim 1 wherein said vapor ductcomprises:

a.' a tubular structure having a flared end adjacent to the boundarybetween said heat input and said heat output zones, the outer edge ofsaid flared end being contiguous with said capillary means, and anarrower end located at a point adjacent to the enclosed end of saidheat pipe in said heat output zone; and

b. said tubular structure having a uniform diameter substantiallysmaller than the inside diameter of said capillary means at all pointsexcept at said flared end.

3. A heat pipe as described in claim 2 wherein said vapor duct includes:

a. a rim around said narrower end of said vapor duct which extendsoutwardly and is curved to form a lip around said narrower end of saidvapor duct; and

b. a configuration of the end of said heat pipe in said heat output zoneforming a reentrant arch of rotation about a point located adjacent toand coaxially with the center of said vapor duct at said narrower end.4. A hea pipe as described in claim 2 wherein said vapor duct isattached to said capillary means at said flared end, and radial bracesextend from said capillary means to said vapor duct adjacent to saidnarrower end of said vapor duct.

5. A heat pipe comprising:

a. a hollow envelope having a sealed wall structure, said wall structureincluding a heat input zone, a heat output zone, and an adiabatic zonebetween said heat input and said heat output zones;

b. capillary means contiguously disposed on at least a portion of theinner surface of said wall structure, said portion including said heatinput, said heat output, and said adiabatic zones;

0. a working medium vaporizable below the operating temperature of saidheat pipe; and

d, a vapor duct mounted within said envelope, said vapor duct having alarger end adjacent to the boundary between said adiabatic and said heatoutput zones, extending into said adiabatic zone, and contiguous withsaid capillary means, and a narrower end located adjacent to theenclosed end of said heat pipe in said heat output zone.

6. A heat pipe as described in claim 5 wherein said vapor ductcomprises:

a. a tubular structure having a narrower end adjacent to the enclosedend of said heat pipe in said heat output region, a flared endterminating in a cylindrical tube having a diameter approximately equalto the inside diameter of said capillary means, said cylindrical tubeextending through said adiabatic zone; and

b. said tubular structure having a uniform diameter substantiallysmaller than the inside diameter of said capillary means at all pointswithin said heat output zone except at said flared end.

7. A heat pipe as described in claim 6 wherein said cylindrical tube atthe flared end of said vapor duct is attached to said capillary meanswithin said adiabatic zone.

8. A heat pipe as described in claim 6 wherein said vapor duct includes:

a. a lip around said narrower end of said vapor duct; and

b. a configuration of the end of said heat pipe in said heat output zoneforming a reentrant arch of rotation about a point located adjacent toand coaxially with the center of said vapor duct at said narrower end.

1. A heat pipe comprising: a. a hollow envelope having a sealed wallstructure, said wall structure including a heat input zone and a heatoutput zone; b. capillary means contiguously disposed on at least aportion of the inner surface of said wall structure, said portionincluding said heat input zone and said heat output zone; c. a workingmedium within said envelope vaporizable below the operating temperatureof said heat pipe; and d. a vapor duct mounted within said envelope,said vapor duct having a larger end adjacent to the boundary betweensaid heat input and said output zones and contiguous with said capillarymeans, and a narrower end located adjacent to the enclosed end of saidheat pipe in said heat output zone.
 2. A heat pipe as described in claim1 wherein said vapor duct comprises: a. a tubular structure having aflared end adjacent to the boundary between said heat input and saidheat output zones, the Outer edge of said flared end being contiguouswith said capillary means, and a narrower end located at a pointadjacent to the enclosed end of said heat pipe in said heat output zone;and b. said tubular structure having a uniform diameter substantiallysmaller than the inside diameter of said capillary means at all pointsexcept at said flared end.
 3. A heat pipe as described in claim 2wherein said vapor duct includes: a. a rim around said narrower end ofsaid vapor duct which extends outwardly and is curved to form a liparound said narrower end of said vapor duct; and b. a configuration ofthe end of said heat pipe in said heat output zone forming a reentrantarch of rotation about a point located adjacent to and coaxially withthe center of said vapor duct at said narrower end.
 4. A heat pipe asdescribed in claim 2 wherein said vapor duct is attached to saidcapillary means at said flared end, and radial braces extend from saidcapillary means to said vapor duct adjacent to said narrower end of saidvapor duct.
 5. A heat pipe comprising: a. a hollow envelope having asealed wall structure, said wall structure including a heat input zone,a heat output zone, and an adiabatic zone between said heat input andsaid heat output zones; b. capillary means contiguously disposed on atleast a portion of the inner surface of said wall structure, saidportion including said heat input, said heat output, and said adiabaticzones; c. a working medium vaporizable below the operating temperatureof said heat pipe; and d. a vapor duct mounted within said envelope,said vapor duct having a larger end adjacent to the boundary betweensaid adiabatic and said heat output zones, extending into said adiabaticzone, and contiguous with said capillary means, and a narrower endlocated adjacent to the enclosed end of said heat pipe in said heatoutput zone.
 6. A heat pipe as described in claim 5 wherein said vaporduct comprises: a. a tubular structure having a narrower end adjacent tothe enclosed end of said heat pipe in said heat output region, a flaredend terminating in a cylindrical tube having a diameter approximatelyequal to the inside diameter of said capillary means, said cylindricaltube extending through said adiabatic zone; and b. said tubularstructure having a uniform diameter substantially smaller than theinside diameter of said capillary means at all points within said heatoutput zone except at said flared end.
 7. A heat pipe as described inclaim 6 wherein said cylindrical tube at the flared end of said vaporduct is attached to said capillary means within said adiabatic zone. 8.A heat pipe as described in claim 6 wherein said vapor duct includes: a.a lip around said narrower end of said vapor duct; and b. aconfiguration of the end of said heat pipe in said heat output zoneforming a reentrant arch of rotation about a point located adjacent toand coaxially with the center of said vapor duct at said narrower end.